"Each booster has a thrust (sea level) of approximately 3,300,000 pounds at launch. They are ignited after the three space shuttle main engines' thrust level is verified. The two SRBs provide 71.4 percent of the thrust at lift- off and during first-stage ascent."

13.7 GW (total)

"Space Shuttle." Grolier Multimedia Encyclopedia. CD-ROM, 1999.

"The orbiter produces up to 470,000 lb of thrust. Two solid rocket boosters produce a thrust of 2.65 million lbs"

9.62 GW(total)

A space shuttle has three distinct modes of flight: liftoff, orbit, and reentry.
The three main parts of the space shuttle are the orbiter itself, the large external
fuel tank, and two solid rocket boosters or SRB's.

At liftoff, when the shuttle is fully fueled. It weighs about 2.0 million
kilograms (without cargo which it can hold a maximum of 29,500 kilograms).
The two solid rocket boosters carry the entire weight of the external fuel tank
and the orbiter, each solid rocket booster weighing in at about 589,569.16 kilograms.
The solid rocket boosters both take the space shuttle to an altitude of 45 kilometers
or 45,000 meters into the sky in about 120 seconds (two minutes) before
they burn out. As they are falling, they sprout three parachutes, and then land
in the ocean for recovery. The solid rocket boosters provide 71.4 percent
of the thrust (1,496,598.64 kilograms) at lift-off while the orbiter's other
three main engines provide the meager 28.6 percent thrust (599,477.9 kilograms)

The overall power of a space shuttle at takeoff is about 12 GW or 12 billion watts of power. That is about 16 million horsepower!

Once the solid rocket boosters detach and the fuel engine detaches, the orbiters
three engines are left to propel the aircraft and its acceleration decreases
substantially.